1. Field of the invention
The present invention relates to an apparatus for and a method of bending a glass sheet heated to its softening point in a furnace, between upper and lower molds.
2. Description of the Prior Art
Various methods and apparatus for producing bent glass sheets for use in automobiles have been known in the art. In such known methods and apparatus, the glass sheet is heated in a furface to its softening point, and the heated glass sheet is fed horizontally by conveyor rolls to a bending station in which the glass sheet is bent to desired shape. U.S. Pat. Nos. 3,476,540 and 3,554,724 to Ritter, Jr., et al reveal glass sheet bending apparatus in which when a heat softened glass sheet is deposited on conveyor rolls in the bending apparatus, a ring-type lower mold member is moved upwardly to cause the glass sheet to sag into conformity with the shaping surface of the lower mold member under inertial and gravitational forces on the glass sheet. U.S. Pat. No. 3,734,706 to Ritter, Jr. discloses a glass sheet bending apparatus including a rapid quenching device for rapidly chilling and tempering a glass sheet as it is bent in the same manner as described above.
In the disclosed apparatus in which the glass sheet is raised off the conveyor rolls by the ring-type lower mold, the glass sheet sags or flexes in its central area heated to the softening point under inertial forces since the ring-shaped shaping surface of the lower mold is inclined towards its center in conformity with the shape of the concave glass sheet. The central area of the glass sheet having the inertia-induced sag remains in contact with the conveyor rolls for a prolonged period of time. Those portions of the glass sheet which are kept in contact with the conveyor rolls are cooled more rapidly than the other glass sheet portions, and are subject to optical defects. U.S. Pat. Nos. 4,197,108 and 4,272,274 to Frank et al show apparatus in which a lower shaping mold is not ring-shaped, but is composed of a solid block having a plurality of elongated shaping members over its entire surface, and the lower shaping mold is lifted to raise the glass sheet off the conveyor rolls for bending the glass sheet on the lower shaping mold. However, inasmuch as the peripheral edge portion of the concave shaping surface of the lower shaping mold, which edge portion is the first surface for the glass sheet to contact, is inclined toward the center of lower shaping mold, the heated glass sheet also tends to sag at its central area under inertial forces when the glass sheet is lifted.
The present invention has been made in an effort to eliminate the aforesaid shortcomings of the conventional apparatus and methods.